{{chembox | Watchedfields = changed | verifiedrevid = 450959568 | Name = Calcium hypochlorite | ImageFile = Calcium hypochlorite.png | ImageClass = skin-invert | ImageSize = | ImageName = Calcium oxychloride | OtherNames = {{ubl|Hypochlorous acid calcium salt|Bleaching powder|Chloride of lime}} | IUPACName = | SystematicName = | Section1 = {{Chembox Identifiers | ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}} | ChemSpiderID = 22912 | InChI = 1S/Cacl.ClO/c;1-2/q+2;2*-1 | SMILES = Cl[O-].[Ca+2].Cl[O-] | InChIKey = ZKQDCIXGCQPQNV-UHFFFAOYAV | StdInChI_Ref = {{stdinchicite|correct|chemspider}} | StdInChI = 1S/Ca.2ClO/c;2*1-2/q+2;2*-1 | StdInChIKey_Ref = {{stdinchicite|correct|chemspider}} | StdInChIKey = ZKQDCIXGCQPQNV-UHFFFAOYSA-N | CASNo = 7778-54-3 | CASNo_Ref = {{cascite|correct|CAS}} | EINECS = 231-908-7 | PubChem = 24504 | RTECS = NH3485000 | UNNumber = 1748 2208 | ChEBI = 31342 | ChEMBL = 2251447 | KEGG = D01727 | UNII = 11DXB629VZ }} | Section2 = {{Chembox Properties | Formula = {{chem2|Ca(OCl)2}} | Ca=1|O=2|Cl=2 | Appearance = white/gray powder | Density = 2.35 g/cm<sup>3</sup> (20 °C) | Solubility = 21 g/(100 mL) at 25 °C | SolubleOther = reacts in alcohol | MeltingPtC = 100 | MeltingPt_notes = | BoilingPtC = 175 | BoilingPt_notes = decomposes }} | Section3 = {{Chembox Hazards | ExternalSDS = [http://www.inchem.org/documents/icsc/icsc/eics0638.htm ICSC 0638] | GHSPictograms = {{GHS03}}{{GHS05}}{{GHS07}}{{GHS09}} | GHSSignalWord = Danger | HPhrases = {{H-phrases|272|302|314|400}} | PPhrases = {{P-phrases|210|220|221|260|264|270|273|280|301+312|301+330+331|303+361+353|304+340|305+351+338|310|321|330|363|370+378|391|405|501}} | NFPA-H = 3 | NFPA-F = 0 | NFPA-R = 1 | NFPA-S = OX | FlashPt = Non-flammable | LD50 = 850 mg/kg (oral, rat) }} | Section4 = | Section5 = | Section6 = |Section8 = {{Chembox Related |OtherAnions = {{ubl|Calcium chloride|Calcium chlorite|Calcium chlorate|Calcium perchlorate}} |OtherCations = {{ubl|Lithium hypochlorite|Sodium hypochlorite|Potassium hypochlorite|Barium hypochlorite|Silver hypochlorite}} |OtherCompounds = {{ubl|Hypochlorite|Chlorine monoxide|Hypochlorous acid|Methyl hypochlorite}} }} }}
'''Calcium hypochlorite''' is an inorganic compound with chemical formula {{chem2|Ca(ClO)2|auto=1}}, also written as {{chem2|Ca(OCl)2}}. It is a white solid, although commercial samples appear yellow. It strongly smells of chlorine, owing to its slow decomposition in moist air. This compound is relatively stable as a solid and solution and has greater available chlorine than sodium hypochlorite.<ref>{{cite web|author1=Gerald F. Connell|title=Key operating strategies for chlorine disinfection operating systems|url=http://www.environmental-expert.com/Files%5C5306%5Carticles%5C13866%5C500.pdf|access-date=19 October 2014}}</ref> "Pure" samples have 99.2% active chlorine. Given common industrial purity, an active chlorine content of 65-70% is typical.<ref name=3V>{{cite web |title=Calcium Hypochlorite - 3V Tech |url=https://www.3v-tech.com/en/technologies-and-solutions/13/calcium-hypochlorite |website=www.3v-tech.com |language=en}}</ref> It is the main active ingredient of commercial products called '''bleaching powder''',{{efn|also '''chlorine powder''', '''chloride of lime''', '''chlorinated lime''', "dry chlorine"}} used for water treatment and as a bleaching agent.<ref name="Ullmann" />
==History== Charles Tennant and Charles Macintosh developed an industrial process in the late 18th century for the manufacture of chloride of lime, patenting it in 1799.<ref name=CWTrench/> Tennant's process is essentially still used today,<ref name=CWTrench/><ref name=Ullmann/> and became of military importance during World War I, because calcium hypochlorite was the active ingredient in trench disinfectant.<ref name=CWTrench>{{cite web|url=https://www.chemistryworld.com/podcasts/calcium-hypochlorite/3008985.article |title=Calcium hypochlorite |publisher=Chemistry World}}</ref>
==Uses== ===Sanitation=== Calcium hypochlorite is commonly used to sanitize swimming pools and disinfect drinking water. Generally the commercial substances are sold with a purity of 65% to 73% with other chemicals present, such as calcium chloride and calcium carbonate, resulting from the manufacturing process. In solution, calcium hypochlorite could be used as a general purpose sanitizer,<ref>{{cite tech report|institution=Mannsvile Chemical Products |date=1987 |title=Chemical Products Synopsis: Calcium Hypochlorite |location=Asbuiy Park, NJ}}</ref> but due to calcium residue (making the water harder), sodium hypochlorite (bleach) is usually preferred.
===Organic chemistry=== Calcium hypochlorite is a general oxidizing agent and therefore finds some use in organic chemistry.<ref>{{cite journal|last1=Nwaukwa|first1=Stephen|last2=Keehn|first2=Philip|title=The oxidation of aldehydes to acids with calcium hypochlorite [Ca(ClO)<sub>2</sub>]|journal=Tetrahedron Letters|date=1982|volume=23|issue=31|pages=3131–3134|doi=10.1016/S0040-4039(00)88577-9}}</ref> For instance the compound is used to cleave glycols, α-hydroxy carboxylic acids and keto acids to yield fragmented aldehydes or carboxylic acids.<ref>{{cite journal|last1=Nwaukwa|first1=Stephen|last2=Keehn|first2=Philip|title=Oxidative cleavage of α-diols, α-diones, α-hydroxy-ketones and α-hydroxy- and α-keto acids with calcium hypochlorite [Ca(ClO)<sub>2</sub>]|journal=Tetrahedron Letters|date=1982|volume=23|issue=31|pages=3135–3138|doi=10.1016/S0040-4039(00)88578-0}}</ref> Calcium hypochlorite can also be used in the haloform reaction to manufacture chloroform.<ref>{{cite book|last1=Cohen|first1=Julius|title=Practical Organic Chemistry for Advanced Students|date=1900|publisher=Macmillan & Co.|location=New York|page=63|url=https://books.google.com/books?id=0xRIAAAAIAAJ}}</ref> Calcium hypochlorite can be used to oxidize thiol and sulfide byproducts in organic synthesis and thereby reduce their odour and make them safe to dispose of.<ref>{{cite book |last1=National Research Council |title=Prudent Practices in the Laboratory: Handling and Disposal of Chemicals |date=1995 |publisher=The National Academies Press |location=Washington, DC |page=161 |doi=10.17226/4911 |bibcode=1995nap..book.4911N |isbn=978-0-309-05229-0}}</ref> The reagent used in organic chemistry is similar to the sanitizer at ~70% purity.<ref>{{cite web |title=8.41799 Calcium hypochlorite for synthesis |url=https://www.sigmaaldrich.com/BE/en/product/mm/841799 |website=Sigma-Aldrich |quote=Assay (iodometric): 67.0 - 75.0 %}}</ref>
==Production== Calcium hypochlorite is produced industrially by reaction of moist slaked calcium hydroxide with chlorine gas. The one-step reaction is shown below:<ref name=Ullmann>{{cite encyclopedia|last1=Vogt|first1=H.|last2=Balej|first2=J|last3=Bennett|first3=J. E.|last4=Wintzer|first4=P.|last5=Sheikh|first5=S. A.|last6=Gallone|first6=P.|last7=Vasudevan|first7=S.|last8=Pelin|first8=K.|year=2010|chapter=Chlorine Oxides and Chlorine Oxygen Acids|encyclopedia=Ullmann's Encyclopedia of Industrial Chemistry|publisher=Wiley-VCH|doi=10.1002/14356007.a06_483.pub2|isbn=978-3527306732|s2cid=96905077}}</ref>
:{{chem2|2 Cl2 + 2 Ca(OH)2 → CaCl2 + Ca(OCl)2 + 2 H2O}}
Industrial setups allow for the reaction to be conducted in stages to give various compositions, each producing different ratios of calcium hypochlorite, unconverted lime, and calcium chloride.<ref name=Ullmann/> In one process, the chloride-rich first stage water is discarded, while the solid precipitate is dissolved in a mixture of water and lye for another round of chlorination to reach the target purity.<ref name=3V/> Commercial calcium hypochlorite consists of anhydrous {{chem2|Ca(OCl)2}}, dibasic calcium hypochlorite {{chem2|Ca3(OCl)2(OH)4}} (also written as {{chem2|Ca(OCl)2*2Ca(OH)2}}), and dibasic calcium chloride {{chem2|Ca3Cl2(OH)4}} (also written as {{chem2|CaCl2*2Ca(OH)2}}).<ref>W.L Smith, Inorganic Bleaches, Production of Hypochlorite in ''Handbook of Detergents,Part F'', (2009) Ed. U Zoller and Paul Sosis, CRC Press, {{ISBN|978-0-8247-0349-3}}</ref><ref>{{cite journal|author=Aleksandrova, M.M.; Dmitriev, G.A.; Avojan, R.L.|title=The probable model of the crystal structure of the twobase calcium hypochlorite|journal=Armyanskii Khimicheskii Zhurnal|year=1968|volume=21|page=380-386}}</ref>
== Reactions == Calcium hypochlorite reacts rapidly with acids producing calcium chloride, chlorine gas, and water:{{cn|date=November 2023}} :{{chem2|Ca(ClO)2 + 4 HCl → CaCl2 + 2 Cl2 + 2 H2O}}
==Safety== It is a strong oxidizing agent, as it contains a hypochlorite ion at the valence +1 (redox state: Cl+1).{{cn|date=November 2023}}
Calcium hypochlorite should not be stored wet and hot, or near any acid, organic materials, or metals. The unhydrated form is safer to handle.{{cn|date=November 2023}}
== See also == * Calcium hydroxychloride * Sodium hypochlorite
==References== {{notelist}} {{reflist}}
{{Calcium compounds}} {{Hypochlorites}}
Category:Antiseptics Category:Bleaches Category:Hypochlorites Category:Calcium compounds Category:Oxidizing agents Category:Household chemicals